Neighbor discovery is disabled and the ISP uses third‑party devices. What must be enabled on the PE router interface Gi1/0 to complete neighbor discovery?

The correct answer is to enable LLDP globally. Link Layer Discovery Protocol (LLDP) is an industry-standard protocol that allows network devices to advertise their identity, capabilities, and neighbors on a local area network. Since the ISP uses third-party devices and neighbor discovery is disabled, LLDP must be enabled to allow the PE router to discover its neighbors. Disabling autonegotiation is unrelated to neighbor discovery. LLDP-MED (Media Endpoint Devices) is an extension of LLDP for IP telephony and is not required for basic neighbor discovery. Disabling Cisco Discovery Protocol (CDP) on the interface is not the solution because CDP is a Cisco proprietary protocol, and the problem states the ISP uses third-party devices, making CDP ineffective for discovery.